They're large, very large, even growing up to 1.5 kilos in size. This is about five times the size of the average black rat, which generally only grow to 200 - 300 grams.

Professor Peter Banks, Assoc Professor in Conservation Biology at the University of Sydney, is conducting a study of the native water rat.

He spoke with ABC Great Southern and says that water rats should be considered our friends and not the dirty rats that we more commonly associate with the term 'rodent'.

The native water rat is prevalent across the entire nation and in fact are the top predators in their murky world, feasting on other small mammals and birds. It may be more helpful to consider the water rat as being a little like otters as they forage and swim in a similar way.

Professor Banks says water rats can even be considered to be cute.

He said, "They don't look like your classic black rats, which people have an aversion to. They have big long whiskers. They have a beautful golden belly and they have a long thick tail that doesn't look ratty at all."

In fact, says Professor Banks, "they have a lot of charisma and a lot of personality."

The rodents live all around the Australian coast and in rivers. They are more common they you think, says Professor Banks. But when people see them, they just think they are big rats and don't bother looking too closely. While they do inhabit industrial ports and urban areas, they are unlikely to be found in your back shed or other domestic areas as the black rat is.

The black rat is an introduced species. Of the two species, it appears the water rat is the dominant one. They are larger and it appears the black rats will avoid the places the water rats inhabit. From the study currently being conducted, there may be evidence that shows the water rats may become an effective form of biological control.

Professor Banks says that, while the study is not yet concluded, it does appear that the water rats do appear to reduce numbers of black rats.

Rakali not rats

"Their aboriginal name is the rakali and that's got some merit to it becuase it doesn't sound so ratty" said Professor Banks.

The rakali is one of many mammals that migrated to the ancient continent about 4 - 5 million years ago. There was a massive migration of mammals at that time, and then another migration to the continent about 1 million years ago. These groups of mammals have since diversified and spread accross all habitats in the country. Today we have a great variety of mice and other rodent species, including the water rat or rakali.

Professor Banks said his study will in future help land managmeent practices that aim to maintain the environment and reduce prevalence of black rats, but there's a lot more to learn about the rakali and its ratty cousins first.